A technology of forming a traveling vehicle group of vehicles equipped with perimeter monitoring devices that monitor the perimeter has been suggested. For example, Patent Document 1 discloses a vehicle group travel control device in which when the vehicles travel as a group, sideward vehicle detection data provided by each vehicle are sent to the leading vehicle, an object vehicle traveling on the adjacent lane within the vehicle group length range is regularly monitored, and when an obstacle is detected in front on the traveling road and the collision therewith cannot be avoided by brake operation, the leading vehicle performs an avoidance scheduling and issues an avoidance method instruction to the following vehicles. As a result, the vehicles that travel cooperatively can travel, while automatically avoiding the obstacle present on the road.    [Patent Document 1] Japanese Patent Application Laid-open No. 2002-266672.